Two enzymes, a cyclic-AMP dependent protein kinase and a phosphoprotein phosphatase, have been purified to near homogeneity from bovine heart. It was discovered that myosin light chains, purified from chicken gizzard can be phosphorylated and dephosphorylated by these two enzymes. The phosphorylation site was characterized anud found to be the same as that phosphorylated by myosin light chain kinase. Other characteristics of this phenomenon were studied and were published this year. Attempts to use the myosin light chains as a substrate for the cascade system were plaqued by their persistent proteolysis, despite extensive efforts to prevent this. Thus a new substrate (a peptide) was custom synthesized and has subsequently been used to determine the kinetic constants which help define cyclic cascade system. Incidentally, some interesting properties of both enzymes have been studied and characterized using this peptide. Meanwhile, a fluorescent peptide was syntheized for use in studies on the kinetic mechanism of protein kinase activation by cAMP. Experiments were carried out with Dr. Vincent Chau which showed the applicability of this peptide to research in this area, and the results have been submitted for publication.